1. One or more Primary parameters, gridded (to 2.5�, for some reason)2. Normals for the Primary parameter(s)3. Normals for the Secondary parameter

The IDL routines do not allow for genuine observations of the secondary parameter to be incorporated.

The problem is that we should be moving towards using secondary observations where available. If we just pick a changeover point, there are likely to be noticeable discontinuities - also we probably don't have enough observations to do that yet!

So, what I propose is this:

1. Produce Secondaries as Secondaries (using synthetically-generated data from Primaries)2. Produce Secondaries as if they were Primaries (ie using direct observations of Secondary values)3. Let the output from 2 overwrite the output from 1 WHERE the actual station count is >=1.

In other words, the synthetic data is replaced with 'genuine' data if there is at least one station reporting within the cell at that timestep.

How does that sound? Any better ideas? It has the advantage that it doesn't require a great deal of coding ;-)